Solvent extraction process



Jan. 30; 1945. R. c, MORRIS ET AL 2,368,597

SOLVENT EXTRACTION .PROCESS I Filed Feb. 8, 1943 Disr'lllafion Column /o Amgl NaPMhalenc 6 8 E9 8 8 9 8 o \o 20 30 .40 50 so To lnvenfora Rupzr C. Morris Alva V. Snider 59 Their Afiornegi Patented Jan. 30, 1945 "UNITED STATE 2,368,59l s PATENT- o Flcsj 2,368,597 SOLVENT sx'rascnom mocnss Rupert 0. Morris, Berkeley, and Alva V. Snider, Richmond, Calif., assignors to Shell Development Company, San Francisco, Calif., a cor- ;poration of Delaware Application February a, 1943, Serial No. 475,211

I 14 Claims. This invention relates to a process for the separation of relatively high boiling organic mixtures by distilling said mixtures in the presence of a sulfolane to change the relative boiling temperatures of the components of the mixture.

It is the broad purpose of this invention to separate relatively-high boiling organic mixtures a of different compounds having similar vapor pressures economically, efliciently and efl'ectively by distillation with a sulfolane to change the relative boiling temperatures of the components of 2 mixtures to be separated in the presence of a sulfolane to form at least one secondary mixture (such as an azeotropic mixture) relatively rich in one of the components of the original mixture, said secondary mixture boiling at a temperature substantially lower than the boiling temperature of said component; (B) separating said secondary mixture or' azeotrope as a vapor from the remainder of the original mixture relatively rich in a different one of the components of said mixture; (C) condensing the vapor and removing the sulfolane from the condensate and usually also recovering the sulfolane removed for further contact with more of said original mixture. These steps, common to all azeotropic distillation processes, may be carried out in any suitable manrler known to those skilledin the art.

- Many diflerent types of relatively high boiling mixtures of organic compounds may be separated with the aid of sulfolanes provided the sulfolane is inert toward the mixture'and the presence of sulfolane in the mixture causes a greaterchange in the boiling temperature of one component of the mixture relative to that of the other components. For economical and complete separation it is desirable that the boiling temperatures of the resulting fractions formed be at least about 3 C. apart. If the original mixture consists of more than two components, such as a petroleum fraction, it isin general desirable that it have a boiling range of not greater thantabout 75C. and preferably less than 50 C.-

In order that low boiling secondary mixtures beformed between the sulfolane and a'component of the original mixture, the boiling temperatures of the sulfrliane and said component must be within about 75 C. of each other, and preferably closer.

High boiling mixtures which ,can be separated comprise petroleum or coal tar 'distillates, fatty acids, fatty acid esters, essential oils and other natural or synthetic organic products having boiling temperatures within the above limits and.

containing components having different degrees.

of saturation and/or polarity. Some specific examples of compounds which may be present in such mixtures and which form different boiling secondary mixtures or azeotropes with sulfolanes are: paraflin, indene, various naphthalenes such as naphthalene from tetrahydronaphthalene and/or decahydronaphthalene, diphenyls, fluorenes, phenanthrene, anthracenes, fluoranthrenes, pyrene, chrysene, etc.; hydrocarbon-oxygen compounds such as phenols, cresols, xylenols, cumenol, mixed alkyl phenols, duranol and naphthols, acetophenones,

alkyl coumarones and diphenylene oxides; hydrocarbon-sulfur compounds such as thionaphthenes and biphenylene sulfide; hydrocarbon-nitrogen compounds such as aniline, alkyl pyridines, quinclines, indols, carbazols, acridine; fatty acids and esters f of fatty acids such as caproic, sorbic,

heptoic, capryllic, capric, undecylic, lauric,

sabinic, myristic', palmitic, margaric, stearic,

oleic, linoleic, ricinoleic, arachatic, behenic, etc., acids; and fruitessences uch as heracleum oil,

banana oil and strawberry, currant, pineapple, raspberry, peach, apple, quince, etc. essences; etc.

The organic sulfolanes employed in the separation of such mixtures include hydrocarbonsubstituted sulfolanessuch as alkyl sulfolanes or derivatives thereof, wherein one or more of the hydrogen atoms in the sulfolane are replaced. by an organic radical which may contain a polar grouping, more speciflcallyan organic radical containing oxygen, sulfur, nitrogen -or halide atoms, provided they are vaporizable without decomposition under the conditions of the process and preferably have melting temperatures below about 150 C. and preferably below about 100 C. It-ispreferred to employ mostly the hydrocarbon, oxygen and sulfur polar groupm a-sulfolene- ,ings in that most nitrogen and halide derivatives as well as some esters and aldehydes are ,rela-' tively heat-unstable even under :reduced' pressures. Further, to meet the stability requirements ofthis invention these sulfolanes should preferably contain not more than two oleflnlc double bonds. v I Some suitable sulfolanes are: sulfolane HaC-.-'-CH| H: I H:

ale-on in an benzpyrenes, naphthacenes,"

the corresponding 2-sulfolenes.

3,4-sulfolanediol, etc.; sulfolanyl ethers such as methyl-3-, propyl-3-, a11y1-3-, butyl-3-, crotyl-3-, isobuty1-3-, methally1-3-, sulfolanyl ethers and corresponding z-sulfolanyl ethers and disulfolanyl ethers, etc.; sulfolanyl esters such as 3- sulfolanyl' acetate, propionate, butyrate, caproate,

etc.; sulfolanyl sulfides such as ethy1-3-, tertiary butyl-3-, isobutyl-3-, methallyl-3-,. folanyl sulfides; di-3-sulfolanyl sulfides, etc.; sulfolanyl .sulfones such as methyl-3-, propyl3-, amyl-3-, etc., sulfolanyl sulfones, and some of and z-sulfolenes may beproduced by condensing conjugated diolefins with sulfur dioxide and then submitting the resultant product to hydrogenation for sulfolanes and isomerization for 2-sul- The sulfolanes admixed with the sulfolane and introduced through feed line I into the side of fractional distillation column 2 provided with reboiler 3 at its bottom. The low boiling azeotrope of A and condenser 5 toliquid phase separator 6. If the folenes, and then further to alkylation, hydration and/or other substitution or addition reactions.

Water vapor and vapors of commonly known selective solvents may be used as auxiliary distillation aids with the sulfolane provided these solvents do not react with the particular sulfolane employed and are stable under the conditions of the process. Some suitable selective solvents which may be employed in conjunction with the sulfolanesinclude: various monoand poIy-hydric alcohols such as methanol, furfuryl,

. glycols, glycerols, etc.; various ketones such as p methyl ethyl ketone, cyclopentanone, benzophenone, etc.; various aldehydes such as crotonaldehyde, fur'fural, etc.; ethers such as ethylene lycol, mono-alkyl ethers, chlorinated dialkyl ethers,dioxane, etc.; lower aliphatic acids, etc.; various phenols; various organic amines such as lower aliphatic primary amines, anilines: etc.;

various nitriles such as lactonitrile, benzonitrile, etc.; various nitro hydrocarbons such as nitromethane, nitrobenzene, etc.; various pyridines and quinolines; various aromatic hydrocarbons such ,as benzene, cumene, anthracene, etc.; and the like. The amount of such additives with the sulfolane must be less than 50% by volume and preferably less than by volume of the sulfolan employed.

The amount of sulfolane added to the high boiling mixture to form a secondary boiling mixture having a sufficient diflierence in boiling temperature from that of said high boiling mixture to make it readily separable by fractional distillation preferably should be enough to form a minimum boiling azeotrope with the component of the original mixture which it is desired to separate from the remainder. A smaller amount will result in incomplete recovery of that component. A greater amount is permissible, since' .the distillation may be controlled so that any excess of sulfolane appears in the bottom product of the distillation.

' Fig. 1 of the accompanying drawing discloses a flow diagram of an azeotropic distillation process which may be employed in carrying out this invention, and Fig. 2 is a graphdepicting the results of azetropic versus ordinary distillation of Example I disclosed later.

Referring to Fig. 1 of the drawing, a mixture to be separated (which for convenience comprises, say, two components A and B, A forming a low boiling azeotrope with the sulfolane) is amount of sulfolane added to the mixture of A and B is not in excess of the amount required to form only an azetrope with component A of said mixture, then pure component B iswithdrawn through valved line 1. sulfolane is added this excess must b removed and the secondary mixture of B and sulfolane is then passed through valved line 8.

In separator 6 the condensed azeotrope of A and sulfolane forms two liquid phases, an upper phase consisting mainly of component A and little sulfolane, and a lower phase consistingmainly of sulfolane and little ofcomponent A. The lower phase is withdrawn through bottom valved line 9 and recycled to column 2 to join feed lin I, thereby aiding in the separation of more of the mixture A and B. A reflux is provided to the top of column 2 from the upper liquid phase in separator 6 through valved line 10 and the remaining portion of theupper phase is withdrawn through line H into scrubber l2 wherein the sulfolane is washed from component A and with some suitable low boiling selective solvent for sulfolanes such as water which is introduced near the top ofscrubber l2 through lin l3. Pure component A is withdrawn from the scrubber I2 through top line l4 and diluted sulfolane is withdrawn through bottom line l5.

This diluted sulfolane is then stripped of its.

water by being passed. through heat exchanger "5 into concentrator I! provided at its bottom with reboiler l8 and at its top with vapor outlet line l9, condenser 20 and accumulator 2| to provide a reflux through valved line 22 and .to discharge the stripped solvent through valved line 23 to waste or through recycle valved line '24, joining line l3 for re-use in scrubber l2. The sulfolane free from solvent is withdrawn from concentrator I! through bottom line 25 which passes through heat exchanger IE to Join the sulfolane in line 9 for recycle to column 2 and to join with mixture A and B in line I. v

, If an excess of sulfolane over that required to form an azeotrope with A is added to the mixture, component B withdrawn from the bottom of distillation column 2 contains sulfolane which must be removed. The secondary mixture of sulfolane and B is then passed through valved line 8 into stripper 26 provided at its bottom with reboiler 21 and at its top with'vapor outlet line 28, condenser 29 and accumulator 30 to provide a reflux through valved line 3| to stripper 26. The sulfolane stripped from component B in column 26 after being collected in accumulator 30 is passed through valved line 32 to join line 9 for recycle to column 2 to join with the mixtureA and B Y in line I. Pure component B is withdrawn from stripper 26 through bottom line 3."

Fresh sulfolane may be added to the'system from time to time as required through valved line 34 joining line 9 and fresh solvent or water may be added ,to the sulfolane recovery system for component A from time to time through valved line 35, joining line IS.

The sulfolane recoverysystems disclosed in Fig. 1 for the secondary mixtures withdrawn from column 2 are merely illustrative of Ways in which However, if an excess of up to about 350 C.

analyzed as shown in hydrocarbon and 75% aseaeor thesuliolane may. be recovered. The sulfolane recovery system for either or both or said secondary mixtures may comprise a water scrubbing system such as shown for the recovery or suitolane from component A, or a stripper as shown for the recovery of sulfolane from component B.

If desired, an azeotropic distillation process similar to that described in Deanesly U. S. Pat-- ent No. 2,290,636 may also be employed.

The pressures employed in the system may naphthalene, v

perature of about 151 C. to.152 C.atv the same pressure.

range from the lowest economical subatmospheric pressure, say about V4 inch of mercury, to atmospheric pressure. Reduced pressures are particularly advantageous when the mixture to be separated is unstable at its normal boiling temperature.

The temperatures employed in distillation column 2 may range anywhere from about 100 C. Mixtures which have normal boiling temperatures above about 350 C. are usually separated at reduced pressures. v

For simplicity, pumps, heat exchangers, by-

passes, vents, pressure release valves, exhausters and other auxiliary equipment have not been shown in the drawing, since their application is evident at once to anyone skilled in the art.

EXAMPLE I A mixture of equal portions by weight of amyl naphthalene and cetane was fractionated through a -inch ring-packed column while maintaining a reflux ratio of approximately 511' under an absolute pressure of about 20 mm. or mercury. This mixture had a boiling range of between about 158 C. and 164 C. During the distillation of this mixture several cuts were taken and the table below. The weight per cent of amyl naphthalene in each cut was plotted against weight per cent of the mixture distilled in Fig. 2 of the drawing whereby curve X was obtained. It can readily be seen from this curve that there was very little if any separation occurred between the amyl naphthalene and the cetane.

- TABLI I Straight fractionation of amyl naphthalenecetane blend -lyzed as high as98.5%

- Approig. Wt. per- Retracpemen Cut No. g 'g 'n wt cent of tive g ggg I charge Index (from R I in cut 1 158-160 14 14 1. 4939 47. 5 2 .160 15. 5 29. 5 1. 4925 46. 5 3-- 160-162 15 44. 5 1. 4912 45. 5 4. 162 15. 5 I 1. 4905 45 5.... 162 16.5- 76.5 1.4915 45.5 6 164 15 91.5 1. 4968 50 Bottoms l0 1. 5343 Amyl naphthalene 166 50 I 1. 5730 Paraiiin hydrocar- Feed 1. 4959 carbon (oetane).- 166 50 l. 4347 A se arate batch containing 100 g. or a mix-' ture of equal portions by thalene and cetane was then mixed with 300 grams of 2,4-dimethyl sulfolane and fractionated at an absolute pressure 0120 mm. of mercury and under a5: 1 reflux through the. same column as'used in the experiment above. It was found that the cetane and 2,4-dimethyl sulfolane formed an azeotrope which, under the pressure employed, boiled at about 142 C., and that phase separation occurred upon cooling this mixture.- The azeotrope consisted approximately of 25% 2,4-dimethyl suliolane...

weight of amyl naphwas formed with the amyl boiled at a tem- Another 'azeotrope which azeotrope seen that an excellent separation between cetane and amyl naphthalene was obtained. the parai' flnic fractions containing as low as"3% naphthalene while the amyl pure amyl naphthalene.

Tarts II Azeotropic distillation of amyl naphthalenecetane mixture with. dimethul .sullolane wt R Per Milt per eamy out No 3% Wt. cent iracnaphthmm 11.0 0111.0 tive alone charged index (from 3.1.)

' in out EXAMPLE II J A mixture of equal parts by weight of methyl 73%. These cuts were analyzed as disclosed in the following table: v

' TABLI: 111

Straight fractionation of methyl naphthalenekerosene blend Wt. r- Relracm Cut No. B. C. g cent i 'tive charge index R L) m 7 cut a a 1.4070 42 1o 18 1. 5150 as 1a 31 1. 6242 no 1a 44 1.5324 s: 11 01 4.5400 11 9 10 1.5508 7:4 0 19 1.5442 10 5 s4 1. 4m '31 o 90 1. 4411 s Bottoms.-- 10 100 r n 10o 1.s1 1o so aromatic fractions ana- The cuts 1 through 8 thus obtained were mixed together to produce a mixture of 78 grams to which mixture was added 100 grams of unsubstituted sulfola'ne and 100 grams of 2,4-dimethyl sulfolane. This resulting blend was then fractionatedat an absolute pressure of 100 mm. and approximately :1 reflux ratio, using the same column as described above. An azeotrope was obtained consisting of approximately 15% sulfolanes and 85% hydrocarbons. During the distillation several cuts were taken and analyzed as shown in the table below.

TABLE IV Azeo troz nc distillation of methyl naphthalenekerosene blend with sulfolane The paraflinic cuts 16 to 23% aromatics, while the aromatic fractions analyzed substantially 100% pure methyl naphthalene.

We claim as our invention:

1. In the process for separating a vaporizable anic mixture of difi'erent components selected from the class consisting of components of different degrees of saturation and components of diflerent degrees of polarity,'comprising distilling said mixture in the presence of a sulfolane stable under the conditions of the process to form I a top product comprising said V sulfolane and a portion of the original mixture relatively rich in one of said components and. a. bottom product comprising the remainder of the original mixture relawere found to contain from Jng the remainder of the original mixture relatively rich in another of said components, sepa- 6 rating said products, and removing said sulfolane from. said top product, said original mixture boiling within C. of said sulfolane.

3. The process of claim 1 wherein said original mixture boils within about 50 C. of said sulfolane.

4. The process of claim 1 wherein said original mixture has a boiling range of less than about 75C.

5. The process of claim 1 wherein said original mixture consists of hydrocarbons.

6. The process of claim 1 wherein said original mixture comprises a lubricating oil.

7. The process of claim 1 wherein said original mixture is selected from the group consisting of fatty acids and fatty acid esters.

8. The process of claim 1 said sulfolane comprising a hydrocarbon-substituted sulfolane.

9. The process of claim 1 said sulfolane comprising a sulfide.

10. The process of claim prising an ether.

11. The process of claim 1 said prising unsubstituted sulfolane.

12. The process of claim 1 said sulfolane comprising 2-4-dimethyl sulfolane. I

13. The process of claim 1 wherein the temperature of distillation ranges between about and about 350 C.

14. The process of claim 1 wherein the pressure for the distillation ranges between about i atmosphereand about 4 inch of mercury.

RUPERT C. MORRIS. ALVA V. SNIDER.

1 said sulfolane comsulfolane com- 

